Solar energy is a promising and abundant source to boost the revelation of renewable energy technology. Despite the remarkable resource potential, its unmatched utilization efficiency is an enormous challenge so far. The conversion of the sunlight to thermal energy, has been the subject of both academic researches and industrialization efforts that have accelerated during the past decade. As consequence, the dramatic increases in energy harvesting efficiency and concomitant decreases in the cost enable many practical applications of solar-thermal energy, such as power generation, domestic heating, brine desalination, and energy conversion processes.
Brine desalination based on solar steam generation, in which the solar absorbers are dispersed in water to directly transfer the heat to water facilitating the evaporation, is not only an efficient way for harvesting the solar energy, but also an effective strategy to resolve the crisis of worldwide fresh water shortage. Since the solar radiation (with flux density of ca. 1,000 W/m2, i.e. one sun) serves as the only power input for the steam generation, it requires a highly efficient solar-thermal energy conversion. In this regard, a variety of materials, including ultra-black absorbers, plasmatic nanoparticles and thermal concentrating ceramics have been explored to enhance the solar-thermal energy conversion efficiency. Nevertheless, the large mismatch between the strong energy demand of water vaporization (i.e. specific heat and latent heat) and the inefficient utilization of converted energy poses another challenge. The energy utilized by water evaporation in air/water interface is effective. However, since the solar absorbers dispersed in water serve as heaters, over 70% of the converted energy is consumed to heat bulk water, which can barely accelerate the water vaporization. Therefore, thermal localization, that is, the confinement of heat to small amount of water in air/water interface (i.e. the evaporating surface), has been proposed to significantly improve the utilization efficiency of solar energy based on the optimized harvesting efficiency. As a result of highly concentrated heating, the heat loss during the energy transport from solar absorber to water becomes a serious problem hindering the further development of solar steam generation. Although the introduction of either optical or thermal concentration system can increase the overall utilization efficiency of solar energy, the ideal method is to realize the highly efficient solar steam generation under one sun or even weaker natural daylight.
There remains a need for water purifiers capable of efficiently converting brine or polluted water into potable water. There remains a need for water purifiers that can efficiently operate using solar energy inputs. There remains a need for water purifiers that are simple to operate and do not require expensive or complicated components.